Spain will vote against the European Union’s draft Brexit deal on Sunday unless it is modified to make clear that the future of the disputed British territory of Gibraltar relies on talks between Madrid and London, Prime Minister Pedro Sanchez said.

Reuters reports that Spain’s demands on Gibraltar are the latest push by EU states to obtain more on national interests ahead of Sunday’s summit of EU leaders, but diplomats said there was little concern these would scupper prospects for a deal.

“As of today, if there are no changes with respect to Gibraltar, Spain will vote no to the agreement on Brexit,” Sanchez said during a conference in Madrid on Tuesday.

According to EU rules, the withdrawal treaty is adopted by qualified majority and not unanimity. So a single state like Spain cannot block it. The EU’s executive said it was aware of Spain’s concerns and it expected the issue to be resolved.